High-bandwidth STO bias architecture with integrated slider voltage potential control

ABSTRACT

Disclosed herein are circuits, architectures, and methods that provide for the control of a data storage device write head&#39;s trailing shield and main pole potential with respect to the disk using circuitry that is integrated with circuitry used to bias a spin torque oscillator (STO) apparatus. Various embodiments include slider connections with STO bias circuitry that resides in a read/write integrated circuit, which has a programmable circuit that generates a bias current with overshoot (bias kicks). Also disclosed are circuits that may be incorporated into a slider to mitigate radio-frequency interference.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of, and hereby incorporates byreference the entirety of, U.S. application Ser. No. 16/537,594, filedon Aug. 11, 2019 and entitled “HIGH-BANDWIDTH STO BIAS ARCHITECTURE WITHINTEGRATED SLIDER VOLTAGE POTENTIAL CONTROL,” which is a continuation ofU.S. application Ser. No. 15/918,060, filed on Mar. 12, 2018 andentitled “HIGH-BANDWIDTH STO BIAS ARCHITECTURE WITH INTEGRATED SLIDERVOLTAGE POTENTIAL CONTROL,” which is a continuation of U.S. applicationSer. No. 15/395,157, filed on Dec. 30, 2016 and entitled “HIGH-BANDWIDTHSTO BIAS ARCHITECTURE WITH INTEGRATED SLIDER VOLTAGE POTENTIAL CONTROL.”As did U.S. application Ser. Nos. 16/537,594, 15/918,060 and 15/395,157,this application also hereby incorporates by reference the entirety ofU.S. nonprovisional application Ser. No. 15/395,111, filed Dec. 30, 2016and entitled “APPARATUS AND METHOD FOR WRITING TO MAGNETIC MEDIA USINGAN AC BIAS CURRENT TO ENHANCE THE WRITE FIELD.”

BACKGROUND

Magnetic storage systems, including data storage devices such as harddisk drives, are used to store large amounts of information. A magnetichead in a magnetic storage system typically includes read and writetransducers for retrieving and storing magnetically encoded informationon a magnetic recording medium, such as a disk.

In a disk-drive system, the read and write transducers reside in aslider that flies over the recording media (e.g., a disk). As storagedensities have increased, and slider fly-heights have decreased, thefly-height of the slider-to-disk spacing has become smaller. Lubricantpickup, corrosion, electrical breakdown, electrostatic discharge (ESD)can all negatively affect the fly-height of the slider. The negativeeffects can be mitigated or eliminated by controlling the slider'svoltage potential with respect to the disk's potential. Controlling theslider's voltage reduces slider wear and allows for lowerflying-heights.

Data storage devices, such as hard disk drives, can suffer fromradio-frequency interference (RFI). The slider body can transfer theseRFI signals to the read transducer, which could damage the readtransducer or interfere with read data signals.

The need to increase storage densities has led to the development oftechnologies such as microwave-assisted magnetic recording (MAMR). InMAMR systems, a spin-torque oscillator (STO) comprising afield-generation layer (FGL) and spin-polarization layer (SPL) is placedwithin in the write gap, and a bias current is supplied to the STO. Inoperation, the write head generates a write field that, beneath the mainpole, is substantially perpendicular to the magnetic recording layer,and the STO generates a high-frequency auxiliary field to the recordinglayer. Ideally, the auxiliary field has a frequency close to theresonance frequency of the magnetic grains in the recording layer tofacilitate the switching of the magnetization of the grains. As aconsequence, the oscillating field of the STO's FGL resonates with themedia and provides strong writing. In addition, the STO's auxiliaryfield may also be used for write field enhancement with the STO mountednear the write head's pole tip.

To generate the auxiliary write field, the STO requires the applicationof a bias voltage that affects the write transducer's pole potential. Inprior-art systems, this bias voltage is DC. Furthermore, the biasvoltage is currently not utilized for controlling the slider's potentialwith respect to the disk's potential. Previous proposals for controllingthe potential of the slider used a dedicated line or shared lines suchas a contact sensor, which has limited functionality through acommon-mode control. There is an ongoing need for methods andapparatuses that control the slider's voltage potential with respect tothe disk's potential while supplying a bias current to a STO in thewrite gap.

SUMMARY

This summary represents non-limiting embodiments of the disclosure.

Disclosed herein are apparatuses and methods for providing a biascurrent to a spin-torque oscillator (STO), and read/write heads and datastorage devices embodying such apparatuses and methods. Some embodimentsprovide for supplying the bias current to the STO while simultaneouslycontrolling the slider's potential with respect to the potential of themagnetic medium. Some embodiments provide for shunting RFI signals onthe slider to ground to mitigate the tendency of these signals to causeread errors. Some embodiments provide for electrically biasing a STO byproviding an AC component (a bias kick) in addition to a low-frequency(e.g., DC) component.

In some embodiments, a circuit for electrically biasing a STO comprisesa first operational transconductance amplifier (OTA), a first low-passfilter coupled to an output of the first OTA and to a first input of thefirst OTA, and a differential current source for providing a STO biaskick current to the STO, the differential current source having firstand second outputs, wherein a second input of the first OTA is coupledto a STO bias voltage source, the output of the first OTA is coupled toa first node of the STO, the first output of the differential currentsource is coupled to the first node of the STO, and the second output ofthe differential current source is coupled to a second node of the STO.In some embodiments, the bias current comprises a low-frequencycomponent and a kick current. In some embodiments in which the biascurrent comprises a low-frequency component and a kick current, one orboth of the low-frequency component and the kick current isprogrammable. In some embodiments, a voltage provided by the STO biasvoltage source is based on a programmed value of the low-frequencycomponent and a resistance of the STO.

In some embodiments, the circuit further comprises an interface voltagecontrol circuit coupled to the STO bias voltage source, wherein a firstnode of the interface voltage control source is coupled to ground and asecond node of the interface voltage control source is coupled to thefirst node of the STO bias voltage source. In some embodiments, thecircuit further comprises a first capacitor and a first terminationresistance connected in series and disposed between and coupled to thesecond input of the first OTA and the first node of the STO. In someembodiments, the circuit further comprises a second capacitor and asecond termination resistance connected in series and disposed betweenand coupled to a second node of the STO bias voltage source.

In some embodiments, the circuit further comprises a first analogcircuit configured to determine a resistance of the STO based on the STObias voltage and a measured STO bias current. In some embodimentsincluding a first analog circuit, the circuit further comprises a secondanalog circuit configured to determine an amplitude of the STO bias kickcurrent based on a voltage provided by the STO bias voltage source, aSTO voltage kick target value, the resistance of the STO, and atermination resistance. In other embodiments including a first analogcircuit, the circuit further comprises firmware configured to determinean amplitude of the STO bias kick current based on a voltage provided bythe STO bias voltage source, a STO voltage kick target value, theresistance of the STO, and a termination resistance.

In some embodiments, the circuit further comprises a second OTA, and asecond low-pass filter coupled to an output of the second OTA and to afirst input of the second OTA, wherein a second input of the second OTAis coupled to the STO bias voltage source, the output of the second OTAis coupled to the second node of the STO, and the STO bias voltagesource is programmable. In some embodiments comprising a second OTA, thecircuit further comprises a capacitor and a termination resistanceconnected in series and disposed between and coupled to the second inputof the second OTA and the second node of the STO.

In some embodiments comprising a second OTA, the circuit furthercomprises a first analog circuit configured to determine a resistance ofthe STO based on the STO bias voltage source and a measured STO biascurrent. In some embodiments comprising a second OTA and a first analogcircuit, the circuit further comprises a second analog circuitconfigured to determine an amplitude of the STO bias kick current basedon a voltage provided by the STO bias voltage source, a STO voltage kickvalue, the resistance of the STO, and a termination resistance. In otherembodiments comprising a second OTA and a first analog circuit, thecircuit further comprises firmware configured to determine the STO biaskick current based on a voltage provided by the STO bias voltage source,a STO voltage kick value, a resistance of the STO, and a terminationresistance.

In some embodiments, a method of electrically biasing a STO comprisesdetermining, using a first analog circuit, a resistance of the STO basedon a STO bias voltage and a measured STO bias current; determining a STObias kick current value based on (a) the resistance of the STO, (b) atermination resistance, and (c) either the STO bias voltage or a STOvoltage kick value; generating the bias current based at least in parton the STO bias current kick value; and providing the bias current tothe STO. In some embodiments, providing the bias current to the STOcomprises supplying the bias current through a push-pull differentialcircuit. In some embodiments, determining the STO bias kick currentvalue based on (a) the resistance of the STO, (b) the terminationresistance, and (c) either the STO bias voltage or the STO voltage kickvalue comprises providing the resistance of the STO, the terminationresistance, and either the STO bias voltage or the STO voltage kickvalue to a second analog circuit. In some embodiments, determining theSTO bias kick current value based on (a) the resistance of the STO, (b)the termination resistance, and (c) either the STO bias voltage or theSTO voltage kick value comprises providing the resistance of the STO andthe STO voltage kick value to firmware, and, using the firmware,calculating the STO bias current kick value. In some embodiments, thebias current comprises a current kick, and generating the bias currentbased at least in part on the STO bias current kick value comprisesdetermining a timing of the current kick based on (i) a positive writesignal transition, (ii) a negative write signal transition, or (iii)both the positive and negative write signal transitions. In someembodiments, the bias current comprises a current kick, and the methodfurther comprises programming a timing of the current kick.

In some embodiments, an apparatus for electrically biasing a STOcomprises means for determining, using a first analog circuit, aresistance of the STO based on a STO bias voltage and a measured STObias current; means for determining a STO bias kick current value basedon (a) the resistance of the STO, (b) a termination resistance, and (c)either the STO bias voltage or a STO voltage kick value; means forgenerating the bias current based at least in part on the STO biascurrent kick value; and means for providing the bias current to the STO.In some embodiments, the apparatus further comprises means forprogramming a timing of the current kick.

In some embodiments, a method for electrically biasing a STO of a writeelement of a magnetic write head in a data storage device comprisesdetermining an amplitude of a high-frequency component of a biascurrent, determining an amplitude of a low-frequency component of thebias current, generating the high-frequency component based at least inpart on the determined amplitude of the high-frequency component,generating the low-frequency component based at least in part on thedetermined amplitude of the low-frequency component, and providing thehigh-frequency and low-frequency components to the STO.

In some embodiments, providing the low-frequency component to the STOcomprises generating the low-frequency component using a voltage source.In other embodiments, providing the low-frequency component to the STOcomprises generating the low-frequency component using a current source.In some embodiments, providing the high-frequency component to the STOcomprises generating the high-frequency component using a currentsource. In some embodiments, the low-frequency component comprises a DCcomponent.

In some embodiments, generating the high-frequency component is furtherbased at least in part on a signal trigger, wherein the signal triggeris determined based on at least one write signal transition. In someembodiments, determining the amplitude of the high-frequency componentcomprises using firmware to calculate the amplitude of thehigh-frequency component based at least in part on a STO resistancevalue. In some embodiments, determining the amplitude of thehigh-frequency component comprises using a circuit to determine theamplitude of the high-frequency component.

In some embodiments, the method further comprises determining a durationof the high-frequency component. In some such embodiments, determiningthe duration of the high-frequency component comprises using firmware todetermine the duration of the high-frequency component.

In some embodiments, generating the low-frequency component is furtherbased at least in part on an indication that the data storage device isin a specified mode. In some such embodiments, the specified mode is awrite mode. In other such embodiments, the specified mode includes atleast one operation other than writing.

In some embodiments, determining the amplitude of the low-frequencycomponent comprises using firmware to calculate the amplitude of thelow-frequency component based at least in part on a STO resistancevalue. In some embodiments, determining the amplitude of thelow-frequency component comprises using a circuit to calculate theamplitude of the low-frequency component.

In some embodiments, the method further comprises jointly optimizing awrite current for writing to a magnetic medium and at least one of thelow-frequency component or the high-frequency component. In someembodiments, the method further comprises programming at least onecharacteristic of the high-frequency component before providing thehigh-frequency component to the STO. In some such embodiments, the atleast one characteristic comprises a delay, an advance, a timing, theamplitude, or a duration of the high-frequency component.

In some embodiments, an apparatus for electrically biasing a STO, thebias current comprising a high-frequency component and a low-frequencycomponent, comprises means for determining an amplitude of thehigh-frequency component, means for determining an amplitude of thelow-frequency component, means for generating the high-frequencycomponent based at least in part on the determined amplitude of thehigh-frequency component, means for generating the low-frequencycomponent based at least in part on the determined amplitude of thelow-frequency component, and means for providing the high-frequency andlow-frequency components to the STO. In some embodiments, the apparatusfurther comprises means for programming a delay or an advance of thehigh-frequency component before providing the high-frequency componentto the STO. In some embodiments, the apparatus further comprises meansfor jointly optimizing a write current for writing to a magnetic mediumand at least one of the low-frequency component or the high-frequencycomponent. In some embodiments, generating the high-frequency componentis further based at least in part on a signal trigger, wherein thesignal trigger is determined based on at least one write signaltransition. In some embodiments, the means for determining the amplitudeof the high-frequency component comprise firmware configured tocalculate the amplitude of the high-frequency component based at leastin part on a STO resistance value. In some embodiments, the means fordetermining the amplitude of the high-frequency component comprise acircuit.

In some embodiments, the apparatus further comprises means fordetermining a duration of the high-frequency component. In some suchembodiments, the means for determining the duration of thehigh-frequency component comprise firmware.

In some embodiments, generating the low-frequency component is furtherbased at least in part on an indication that the data storage device isin a specified mode. In some embodiments, the specified mode is a writemode. In some embodiments, the specified mode includes at least oneoperation other than writing.

In some embodiments, the means for determining the amplitude of thelow-frequency component comprise firmware configured to calculate theamplitude of the low-frequency component based at least in part on a STOresistance value. In some embodiments, the means for determining theamplitude of the low-frequency component comprise a circuit.

In some embodiments, the apparatus further comprises means for jointlyoptimizing (a) a write current for writing to a magnetic medium and (b)at least one of the low-frequency component or the high-frequencycomponent.

In some embodiments, the apparatus further comprises means forprogramming at least one characteristic of the high-frequency componentbefore providing the high-frequency component to the STO. In some suchembodiments, the at least one characteristic comprises a delay, anadvance, a timing, the amplitude, or a duration of the high-frequencycomponent.

In some embodiments, a circuit to control potential of a slider body ina data storage device comprises a first resistance disposed between andcoupled to the slider body and a first node of a STO of a magnetic writeelement, a second resistance disposed between and coupled to the firstnode of the STO and a second node of the STO, and a shunt circuitcoupled to and disposed between the slider body and a system groundpotential. In some embodiments, the shunt circuit comprises a firstbranch comprising a third resistance, and a second branch comprising acapacitance, wherein the first and second branches are connected inparallel. The third resistance may be approximately 750 kOhms, and thecapacitance is preferably greater than or equal to approximately 40 pF.

In some embodiments, the first node of the STO is a trailing shield ofthe magnetic write element, and the second node of the STO is a mainpole of the magnetic write element. In some embodiments, the shuntcircuit is coupled to a first read line of a read element through athird resistance and to a second read line of the read element through afourth resistance, and the third and fourth resistances are coupled by afifth resistance connected in parallel to the first and second read lineof the read element. The third and fourth resistances may beapproximately 15 kOhms, and the fifth resistance may be approximately 2kOhms. In some embodiments, the shunt circuit is coupled to a first lineof an embedded contact sensor through a third resistance and to a secondline of the embedded contact sensor through a fourth resistance. Thethird and fourth resistances may be approximately 18 kOhms.

In some embodiments, an apparatus for electrically biasing a STOcomprises means for determining, using a first analog circuit, aresistance of the STO based on a STO bias voltage and a measured STObias current; means for determining a STO bias kick current value basedon (a) the resistance of the STO, (b) a termination resistance, and (c)either the STO bias voltage or a STO voltage kick value; means forgenerating the bias current based at least in part on the STO biascurrent kick value; and means for providing the bias current to the STO.In some embodiments, the apparatus further comprises means forprogramming a timing of the current kick.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure herein is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings, in whichlike reference numerals refer to similar elements and in which:

FIG. 1 illustrates several components of an exemplary hard disk drive inaccordance with some embodiments.

FIG. 2 is a simplified drawing of an apparatus 100 for writing to amagnetic medium in accordance with some embodiments.

FIG. 3A illustrates an electrical shunt configuration that may beimplemented in the slider to control the potential of the slider bodywith respect to ground and the disk potential in accordance with someembodiments.

FIG. 3B illustrates an alternative slider shunt configuration inaccordance with some embodiments.

FIG. 4 illustrates a circuit for biasing both the slider potential andthe potential of the resistive STO element.

FIG. 5 illustrates the determination of the appropriate STO bias kickcurrent value in accordance with some embodiments.

FIG. 6 shows an exemplary write current and exemplary voltage kicks inaccordance with some embodiments.

FIG. 7 illustrates an architecture in which timing for the bias kick isdetermined based on the input write data transitions and a programmabledelay.

FIG. 8 is a flowchart illustrating a method of electrically biasing aSTO in accordance with some embodiments.

FIG. 9 is a flowchart illustrating a method of electrically biasing aSTO in accordance with some embodiments.

DETAILED DESCRIPTION

The following description is made for the purpose of illustrating thegeneral principles of the present disclosure and is not meant to limitthe inventive concepts claimed herein. Furthermore, particularembodiments described herein may be used in combination with otherdescribed embodiments in various possible combinations and permutations.

The “Background” section above described a “classical” STO. U.S. patentapplication Ser. No. 15/140,761, filed Apr. 28, 2016 and herebyincorporated by reference, discloses writers with spin-torque-assistedwrite field enhancement that use a DC-field-generation (DFG) layer tocreate an auxiliary magnetic field that adds constructively to the writefield and thereby enables high-density magnetic recording. A significantbenefit of writers that use a DFG layer is that they enable high-densitymagnetic recording without requiring resonance with the media.Consequently, there is no need to jointly optimize the writer and themedia of the disk drive as there would be to achieve high performancewith a MAMR writer.

As with the “classical” STO, generating the auxiliary field using theDFG layer approach of application Ser. No. 15/140,761 requires theapplication of a bias voltage that affects the write transducer's polepotential. In addition, an overshoot may be desirable to improve theperformance of a write head using a STO or DFG layer, but providing suchan overshoot requires high-speed circuits with a high-bandwidthelectrical interconnect, which can adversely affect the reliability ofthe STO if not set properly from the write signal's crosstalk to theSTO. As discussed in the “Background” section, several undesirableeffects can be mitigated or eliminated by controlling the slider'svoltage potential with respect to the disk's potential. Therefore, thereis an ongoing need for methods and apparatuses that control the slider'svoltage potential with respect to the disk's potential while supplying abias current with overshoots to a STO or DFG layer apparatus in thewrite gap.

Disclosed herein are circuits, architectures, and methods that providefor the control of the write head's trailing shield and main polepotential with respect to the disk using circuitry that is integratedwith circuitry used to bias a STO or DFG apparatus. A unique sliderarchitecture and circuit enable control of the potential of the writehead's main pole and trailing shield with respect to the disk, withoptional electrical connection to nearby transducers and slider. Variousembodiments include slider connections with STO/DFG apparatus biascircuitry that resides in a read/write integrated circuit, which has aprogrammable circuit, referred to herein as a bias kick circuit, thatgenerates a bias current with overshoot (bias kicks) and that allowsshort bias steps during write transitions. Also disclosed are circuitsthat may be incorporated into a slider to mitigate radio-frequencyinterference.

Although a magnetic write head using a DFG layer as described in U.S.application Ser. No. 15/140,761, discussed above, differs from amagnetic write head using a “classical” STO, discussed in the“Background” section herein, for convenience this document refers toboth approaches as “STO.” It is to be understood that the disclosuresherein apply not only to embodiments using “classical” STO but also toembodiments using the DFG layer approach described in application Ser.No. 15/140,761.

FIG. 1 is a top plan view of a head/disk assembly of a hard disk drive10 with the cover removed. The disk drive 10 includes a rigid base 12supporting a spindle 14 that supports at least one disk 16. The spindle14 is rotated by a spindle motor (not shown), which, in operation,rotates the at least one disk 16 in the direction shown by the curvedarrow 17. The hard disk drive 10 has at least one load beam assembly 20having an integrated lead suspension (ILS) or flexure 30 with an array32 of electrically conductive interconnect traces or lines. The at leastone load beam assembly 20 is attached to rigid arms 22 connected to anE-shaped support structure, sometimes called an E-block 24. The flexure30 is attached to an air-bearing (or, in the case that helium or anothergas is used instead of air inside the disk drive, a gas-bearing) slider28. A magnetic recording read/write head 29 is located at the end ortrailing surface of slider 28. The flexure 30 enables the slider 28 to“pitch” and “roll” on an air (or gas) bearing generated by the rotatingdisk 16.

The disk drive 10 also includes a rotary actuator assembly 40rotationally mounted to the rigid base 12 at a pivot point 41. Theactuator assembly 40 is a voice coil motor (VCM) actuator that includesa magnet assembly 42 fixed to the base 12 and a voice coil 43. Whenenergized by control circuitry (not shown), the voice coil 43 moves andthereby rotates E-block 24 with attached arms 22 and the at least oneload beam assembly 20 to position the read/write head 29 over the datatracks on the disk 16. The trace interconnect array 32 connects at oneend to the read/write head 29 and at its other end to read/writecircuitry contained in an electrical module or chip 50, which, in theexemplary disk drive 10 of FIG. 1, is secured to a side of the E-block24. The chip 50 includes a read/write integrated circuit (R/W IC),certain functions of which are discussed below in the context of certainembodiments.

As the disk 16 rotates, the disk 16 drags air under the slider 28 andalong the air-bearing surface (ABS) of the slider 28 in a directionapproximately parallel to the tangential velocity of the disk 16. As theair passes under the ABS, air compression along the air flow path causesthe air pressure between the disk 16 and the ABS to increase, whichcreates a hydrodynamic lifting force that counteracts the tendency ofthe at least one load beam assembly 20 to push the slider 28 toward thedisk 16. The slider 28 thus flies above the disk 16 but in closeproximity to the surface of the disk 16.

In operation, after the voice coil 43 has positioned the read/write head29 over the data tracks on the disk 16, the read/write head 29 may beused to write information to one or more tracks on the surface of thedisk 16 and to read previously-recorded information from the tracks onthe surface of the disk 16. Processing circuitry in the hard drive 10provides to the read/write head 29 signals representing information tobe written to the disk 16 and receives from the read/write head 29signals representing information read from the disk 16.

To read information from the disk 16, the read/write head 29 may includeonly one read sensor, or it may include multiple read sensors. The readsensor(s) in the read/write head 29 may include, for example, one ormore giant magnetoresistance (GMR) sensors, tunneling magnetoresistance(TMR) sensors, or another type of magnetoresistive sensor. When theslider 28 passes over a track on the disk 16, the read/write head 29detects changes in resistance due to magnetic field variations recordedon the disk 16, which represent the recorded bits.

FIG. 2 is a simplified drawing of an apparatus 100 for writing to amagnetic medium, such as the disk 16, in accordance with someembodiments. The apparatus 100 includes a STO 120 disposed in the writegap between a main pole 110 and a trailing shield 130 of a write head.As explained previously, the STO 120 may be a conventional STO (i.e.,including a STL and a FGL), or it may be in a configuration that uses aDFG layer as described in U.S. application Ser. No. 15/140,761. Twonodes or contacts for supplying the STO bias current to the STO 120 areshown. A first node, labeled “A,” is connected to the trailing shield130, and a second node, labeled “B,” is connected to the main pole 110.The apparatus 100 also includes a write coil 112 wound around a magneticcircuit that includes the main pole 110 and the trailing shield 130. Theapparatus 100 also includes a STO bias circuit 200, which supplies thebias current 160 to the STO 120 through the nodes A and B, and a writecurrent control circuit 190, which supplies the write current 162 to thewrite coil 112 through the nodes labeled “C” and “D.” As indicated bythe dashed line, the STO bias circuit 200 and the write current controlcircuit 190 may be communicatively coupled (i.e., the STO bias circuit200 may be able to receive signals or information from the write currentcontrol circuit 190).

The main pole 110 is typically made from a high-saturation magnetizationmaterial for generating a write field that is substantiallyperpendicular to the surface of the magnetic disk over which the slider28 flies. Away from the ABS 105, the main pole 110 and trailing shield130 are coupled by a nonconductive material 118 (e.g., aluminum oxide oranother nonconductive material) that also electrically insulates themain pole 110 from the trailing shield 130.

The write coil 112 is connected to the write current control circuit190, which may be implemented in a R/W IC. In order to write to themagnetic medium, the write current control circuit 190 supplies a writecurrent to the write coil 112. The write coil 112 magnetizes the mainpole 110 and causes the main pole 110 to generate a write field that issubstantially perpendicular to the ABS 105, which then interacts withthe magnetic medium 520 to record information onto the magnetic medium520. The polarity of the generated field causes a region of the magneticdisk 16 to assume a polarity, thus enabling information to be stored onthe disk 16.

The STO 120, which is disposed in the write gap between the main pole110 and the trailing shield 130, is coupled to the STO bias circuit 200through the main pole 110 and the trailing shield 130 at, respectively,nodes B and A. The driving current control circuit 200 may beimplemented in a R/W IC as discussed below in the context of FIG. 7. Asexplained previously, when an appropriate bias current 160 is suppliedto the STO 120, the STO 120 generates an auxiliary magnetic field in thedisk 16 that adds constructively to the magnetic field generated by themain pole 110 and thereby improves the performance of the writer.

As will be understood by a person having ordinary skill in the art, thetrailing shield 130 is a significant physical part of the write elementstructure that is exposed to the ABS 105. Thus, typically, the STO biascircuit 200 applies a positive voltage to the trailing shield 130, nodeA, as compared to the main pole 110, node B. It is to be understood thatin some embodiments, a programmable bit may be used to reverse the STObias polarity. All of the design principles disclosed herein remainapplicable to such embodiments.

At least some embodiments described herein allow existing signal pathson the slider 28 to be employed to perform their existing functions,such as supplying the STO bias current 160 to the STO 120 or an embeddedcontact sensor signal to an embedded contact sensor, while also beingused in an integral fashion to couple a bias voltage to the body of theslider 28, and, in some embodiments, to control or attenuate RFIsignals. As sliders have become very small, there is often little or nophysical space on the slider 28 to add additional signal paths. At leastsome of the embodiments described herein provide for slider 28 biasingand RFI interference immunity or attenuation by using existing signalpaths.

The disclosed architecture is referred to herein as an integratedSTO-bias kick (ISBK) architecture. In some embodiments, the ISBKarchitecture has slider shunt connections that connect to the existingSTO bias lines and control the slider potential. In some embodiments,the slider 28 includes a high-frequency low-impedance path to provideRFI immunity. In some embodiments, the slider 28 has transducerconnections to a common electrical connection that connects to the STObias line(s) to electrically bias the STO. In some embodiments (e.g., asshown in FIG. 7), the hard disk drive includes a R/W IC that includes aSTO bias circuit 200 to provide high-speed bias kicks (overshoot) toimprove STO 120 reliability, including, in some embodiments one or moreof the following: (i) an electrical circuit to produce STO bias kicks;(ii) a STO bias kick signal trigger from a write data signal input;(iii) a programmable timing delay offset from a write signal input andSTO bias kick transition; (iv) differential STO bias kick crosstalkmitigation; and/or (v) a high-bandwidth interconnect for delivering biaskicks to the STO 120. As explained below, the disclosed architecturesprovide for either current biasing or voltage biasing. In someembodiments, the R/W IC's STO bias circuit 200 provides the bias for thewrite trailing shield 130 and main pole 110 and other transducers. Insome embodiments, the bias potential is controllable with respect to themedia and is limited in value so as to prevent head-to-disk breakdowndamage (<1 Volt), and/or current-limit protection is provided forconductive asperities to the disk.

As used herein, the phrase “existing signal path” refers to using anexisting signal path, such as a STO bias current 160 path or an embeddedcontact sensor path, to couple the bias voltage to slider 28 body. Asexplained below, the existing signal path may be slightly modified, suchas through the inclusion of components such as a capacitance, a couplingto a slider 28 body connection, and/or a resistance, but there is noneed for a separate special purpose signal path for coupling the sliderbias voltage from slider bias voltage generator to the slider body. Asused herein, the term “integrated” means that the existing signal pathis primarily used for conveying another signal (e.g., a STO bias current160 or embedded contact sensor signal) between the slider 28 and someentity external to the slider 28. At least sometimes, however, the othersignal and a slider bias voltage are conveyed simultaneously, integratedtogether with one another, on the same signal path within the slider 28.Thus, this existing signal path may convey the bias voltage to theslider 28 body along with the other signal (e.g., STO bias current 160or embedded contact sensor signal) that is being conveyed on the samesignal path.

FIG. 3A illustrates a configuration that is implemented in the slider 28to control the potential of the slider 28 body with respect to groundand the disk 16 in accordance with some embodiments. The slider 28 hasconductive connections and includes a write coil 112, a read element270, a STO 120, an embedded contact sensor 275, and a thermal fly-heightcontrol element 280. As shown, each of the elements is associated withslider pads configured to connect to signal lines from an externalintegrated circuit (IC). Thus, each of the write coil 112, read element270, and embedded contact sensor 275 includes input/output pads denoted,respectively, as W+ and W−, R+ and R−, and E+ and E−. The thermalfly-height control element 280 has input/output pads denoted as T andTgnd, where Tgnd is connected to ground in this exemplary embodiment.

The thick line represents the slider body connection 260. As shown inFIG. 3A, the write coil 112 is floating. Optionally, a capacitance 235Bmay be connected in parallel between the write lines W+ and W− throughnodes C and D. If present, the capacitance 235B has a value ofapproximately 3 pF.

FIG. 3A includes a shunt circuit 265 disposed between the slider bodyconnection 260 and ground (node 310). The shunt circuit 265 comprises aresistance 230H connected in parallel with a capacitance 235A in serieswith two parasitic resistances 285A and 285B. The capacitance 235Ashunts RFI signals from the slider 28 body through the capacitance 235Ato ground through node 310, thus reducing or eliminating the RFI signalsand, at the same time, reducing or attenuating the coupling of RFIsignals to the read element 270. The shunt circuit 265 thereby providesRFI suppression of high-frequency signals that have coupled into theslider 28 body. As will be understood by skilled artisans, the values ofthe capacitance 235A and the resistance 230H may be selected to achievean appropriate cutoff frequency, fc, for shunting RFI signals using theequation C=1/(2*pi*R*fc). In some embodiments, the resistance 230H isapproximately 750 kOhms, the capacitance 235A is greater than or equalto 40 pF, and the sum of the parasitic resistances 285A and 285B is lessthan about 10 Ohms. The shunt circuit 265 creates a path to ground (node310) for AC signals (e.g., signals having frequencies above a selectedcutoff frequency) that might otherwise degrade the performance of thehard disk drive 10. For example, when the shunt circuit 265 is includedin the slider 28, RFI signals that might otherwise travel to the readelement 270, thereby potentially adding interference signals to the readsignals and creating possible read errors, are shunted to ground (node310).

To control the resistance of the read element 270, a resistance 230G isconnected in parallel with the read element 270 between the read linesR+ and R−. For preventing electrical charge build up during processing,a resistance 230E is connected between the node 310 and the read lineR+, and a resistance 230F is connected between the node 310 and the readline R−. Preferably, the resistances 230E and 230F have values ofapproximately 15 kOhms, and the resistance 230G has a value ofapproximately 2 kOhms. Similarly, for preventing electrical chargebuildup, the embedded contact sensor 275 has a resistance 230C connectedbetween the node 310 and the embedded contact sensor line E−, and aresistance 230D connected between the node 310 and the embedded contactsensor line E+. Preferably, the values of the resistances 230C and 230Dare approximately 18 kOhms.

In addition to mitigating RFI interference, the configuration of FIG. 3Aalso provides an asymmetric circuit that allows integrated, single-endedcontrol of the trailing shield 130 potential through the node A. Asexplained above, the STO 120 is connected to the main pole 110 and thetrailing shield 130 through, respectively, the nodes B and A. Aresistance 230A is connected in parallel between the nodes A and B, anda resistance 230B is connected between the node A and the slider bodyconnection 260. Preferably, the values of the resistances 230A and 230Bare approximately 18 kOhms. As explained elsewhere, the nodes A and Bare connected to a STO bias circuit 200, described below in more detail.Thus, although the primary purpose of the nodes A and B is to providethe STO bias current 160 to the STO 120, in some embodiments, the nodesA and B are also used to couple the slider bias voltage to the slider 28body. When writing occurs (e.g., when the hard disk drive is in a writemode), the STO bias current 160 and slider bias voltage can be conveyedsimultaneously through the nodes A and B. When no writing is takingplace (e.g., when the hard disk drive is in a mode that does not includewriting), the nodes A and B may be used solely to bias the slider 28.

FIG. 3B illustrates an alternative electrical shunt configuration thatis implemented in the slider 28 to control the potential of the slider28 body with respect to ground and the disk 16 potential in accordancewith some embodiments. As in FIG. 3A, the write coil 112 is floating.Optionally, a capacitance 235B may be connected in parallel between thewrite lines W+ and W− through nodes C and D. If present, the capacitance235B has a value of approximately 3 pF.

Like FIG. 3A, FIG. 3B includes a shunt circuit 265 disposed between theslider body connection 260 and ground (connected to node 310). The shuntcircuit 265 of FIG. 3B is identical to the shunt circuit 265 of FIG. 3Aand provides the same benefits.

Also as in FIG. 3A, a resistance 230E is connected between the node 310and the read line R+, a resistance 230F is connected between the node310 and the read line R−, and a resistance 230G connected in parallelwith the read element 270 between the read lines R+ and R−. Preferably,the resistances 230E and 230F have values of approximately 15 kOhms, andthe resistance 230G has a value of approximately 2 kOhms.

As explained previously, the STO 120 is connected to the main pole 110and the trailing shield 130 through, respectively, the nodes B and A. Inthe configuration of FIG. 3B, a resistance 230A is connected in parallelbetween the nodes A and B, and a resistance 230B is connected betweenthe node A and the node 310. Preferably, the values of the resistances230A and 230B are approximately 18 kOhms.

In the embodiment of FIG. 3B, the common mode of the embedded contactsensor 275 is used to control the potential of the slider 28, and thetrailing shield 130 is kept at ground potential. A resistance 230Cconnected between the slider body connection 260 and the embeddedcontact sensor line E− and a resistance 230D connected between theslider body connection 260 and the embedded contact sensor line E+.Preferably, the values of the resistances 230C and 230D areapproximately 18 kOhms. Thus, although the primary purpose of the linesE+ and E− is to provide signals to the embedded contact sensor, in someembodiments, the lines E+ and E− are also used to couple the slider biasvoltage to the slider body.

FIG. 4 illustrates a STO bias circuit 200 for biasing both the slider 28potential, at node A, and the potential of the STO 120, which is thedifferential potential between node A and node B, in accordance withsome embodiments. For example, the STO bias circuit 200 shown in FIG. 4may be used in conjunction with the exemplary configuration illustratedin FIG. 3A to bias the slider 28 body and provide the STO bias current160 through the nodes A and B. The STO bias circuit 200 uses feedback toset the DC level (e.g., the amplitude of a low-frequency or DCcomponent) of the STO bias current 160 supplied to the STO 120. In someembodiments, the STO bias circuit 200 resides in a R/W IC (e.g., asshown in FIG. 7). The STO bias circuit 200 includes a first operationaltransconductance amplifier (OTA) 210A and a second OTA 210B. As would beappreciated by a person having ordinary skill in the art, an OTA is anamplifier that converts a differential input voltage to an outputcurrent. An OTA typically has a high input impedance and a high gain,though a high gain is not a requirement (i.e., the gain may be a lowerlevel). The first OTA 210A has two inputs, shown as “+” and “−” in FIG.4, and one output. A low-pass filter (LPF) 215A is coupled to the “−”input of the first OTA 210A and to the output of the first OTA 210A.Similarly, the second OTA 210B has two inputs, shown as “+” and “−” inFIG. 4, and one output. A LPF 215B is coupled to the “−” input of thesecond OTA 210B and to the output of the second OTA 210B. Preferably,the cutoff frequencies of the LPFs 215A and 215B are tens of MHz. The“+” inputs of both the first OTA 210A and the second OTA 210B arecoupled to a STO bias voltage source 205. The “+” input of the first OTA210A and the STO bias voltage source 205 are also coupled to aninterface voltage control (IVC) circuit 220. The IVC circuit 220provides the slider bias voltage, and the STO bias voltage source 205provides the DC level (e.g., the amplitude of the low-frequency (e.g.,DC) component) of the STO bias current 160. A first capacitance 235C anda first resistance 230J (e.g., with a value equal to half of thetermination resistance, Rterm) are connected in series between the “+”input of the first OTA 210A and node A. A second capacitance 235D and asecond resistance 230K are connected in series between the “+” input ofthe second OTA 210A and node B. A differential current source,represented by the current sources 225A and 225B, is also coupled tonodes A and B to provide the STO bias kick to the STO 120. Thus, the STObias circuit 200 of FIG. 4 enables the simultaneous control of theslider 28 potential and supply of the STO bias current 160 with biaskicks through the nodes A and B.

In some embodiments, such as the embodiment illustrated in FIG. 3A, nodeA is connected to the slider 28 body through a resistance 230B, and thefirst OTA 210A is used as a voltage follower with the IVC circuit 220potential. By using the LPF 215A in the feedback loop of the first OTA210A, the output impedance is relatively high as compared to thetermination resistances 230J and 230K in the high-frequency region(e.g., >100 MHz). At high frequencies, the LPFs 215A and 215B blocksignals and act as an open circuit. This high-frequency condition thenallows for good transmission line termination for the high-bandwidthinterconnect while providing current kicks to the STO 120. Similarly,the voltage of the STO bias voltage source 205 is imposed on theresistance of the STO 120 by the second OTA 210B and LPF 215B. Thevoltage bias kick (overshoot) can then be applied by the differentialcurrent sources 225A and 225B. The use of a differential kick ispreferred to reduce the crosstalk of adjacent signal paths on the ILS orflexure 30.

With all of the components shown in FIG. 4 enabled, the STO bias circuit200 uses voltages and the differential current sources 225A and 225B tobias the STO 120. The STO bias circuit 200 may also be used to implementan all-current STO bias. In such embodiments, the kick current sources225A and 225B provide a low-frequency component (which may be eitherpurely DC or may include a low-frequency AC component) in addition tothe kick current, where the low-frequency component is added to the kickcurrent. In such embodiments, the first OTA 210A and the LPF 215A areenabled, and the OTA 210B and LPF 215B are disabled or are eliminatedaltogether from the STO bias circuit 200 of FIG. 4. Such embodimentsallow for an all-current bias scheme for the STO 120.

When the bias current 160 comprises a low-frequency (e.g., DC) componentand a kick current, the low-frequency component may be programmable(e.g., the voltage provided by the STO bias voltage source 205 may bebased on a programmed value of the low-frequency component and aresistance of the STO 120).

To improve the reliability of the STO 120, a voltage bias kick may bepreferred over a current kick. FIG. 5 is a block diagram of a STO biaskick calculation circuit 245 that determines the appropriate STO biaskick current value, denoted as Ikick, in accordance with someembodiments. Using a first analog circuit 250 (also referred to hereinas an intrinsic circuit), the resistance of the STO 120, denoted asRsto, is calculated using the values of a measured STO bias current 160,denoted as Ib′, and the voltage, Vsto, provided by the STO bias voltagesource 205. The Rsto value, with the termination resistance value(Rterm), and the Vkick value or percentage of Vsto are then processed bythe block 255 to calculate the Ikick value. As indicated by FIG. 5, theblock 255 may be a second analog circuit (a second intrinsic circuit) orfirmware functionality executed by a processor (referred to hereinsimply as “firmware”). The Ikick bias may then be supplied to the nodesA and B using a push-pull differential circuit that creates bias pulses(e.g., the circuit 200 shown in FIG. 4).

FIG. 6 illustrates an exemplary write current 162 along with an exampleof the voltage kicks. The DC level of the differential Vsto bias(labeled as Vsto_diff in FIG. 6) is 300 mV and the Vkick value is 200mV. The values shown in FIG. 6 are typical offset values for the IVCvoltage, Vsto+=−200 mV, and the low potential of the main pole 110,Vsto−=−500 mV. As illustrated, the voltage kicks are offset from thepulses of the write current 162 by a delay that is equal to D1−D2, whereD1 is the delay of the write path and D2 is the delay of the STO biaskick, both of which are discussed below in the context of FIG. 7. Insome embodiments, the offset between the STO kicks and the pulses of thewrite current 162 is programmable.

FIG. 7 shows a high-level architecture that illustrates the embodimentsof FIGS. 4 and 5 in the context of the channel 295, part of the systemon a chip (SoC), and the R/W IC 300. As illustrated, in someembodiments, the STO bias circuit 200 and the STO bias kick calculationcircuit 245 are incorporated into the R/W IC 300. The output of the STObias kick calculation circuit 245 is the kick current, Ikick, and theSTO bias circuit 200 generates the STO bias current 160 as describedpreviously in the context of FIGS. 4-6. The STO bias current 160includes Ikick and may be provided by the STO bias voltage source 205and the IVC circuit 220 in conjunction with the embodiment illustratedin FIG. 3A. The output of the STO bias circuit 200 is then delayed by aprogrammable delay block 305B. The STO bias kick path has an inherentcircuit delay denoted as D2, a part of which is the delay caused by theprogrammable delay block 305B. Delay blocks 305A and 305B may beconfigured to provide a substantial amount of offset time, such thatadequate time is allowed for presetting the high-speed circuits thatcreate the current kick amplitude and shape, for example, the rise/falltime. Shown in FIG. 6 is the STO differential bias kick, where the kickprecedes the write current transition, but it is to be appreciated thatthe kick may follow or coincide with the write current transition. Thearchitectures and methods disclosed herein provide significantflexibility in the timing (e.g., relative to a write pulse of the writecurrent 162) and characteristics (e.g., amplitude, duration, shape,etc.) of the bias kicks. The examples discussed and illustrated hereinare not intended to be limiting.

The channel 295 includes a write data process block and write patternlogic coupled to a write buffer. The output of the channel 295 entersthe R/W IC 300, which includes a write path. The write path has aninherent circuit delay denoted as D1, a part of which is the delay ofthe programmable delay block 305A.

In the exemplary embodiment of FIG. 7, the timing for the bias kickcurrent Ikick is determined based on a write trigger, on either or bothof the positive and negative write transitions, and the delays of theprogrammable delay blocks 305A and 305B. Preferably, the delays D1 andD2 are designed to be independent of temperature, such thatenvironmental changes will not affect the pre-programmed delay offsets.The characteristics (e.g., amplitude, duration, transitions, frequency,duty cycle, etc.) of the write current 162 and the bias current 160 maybe jointly optimized to achieve the desired performance.

FIG. 8 is a flowchart illustrating a method 400 of electrically biasinga STO 120 in accordance with some embodiments (e.g., as shown in FIGS. 4and 5). At 405, the process begins. At 410, the resistance Rsto of theSTO 120 is determined by the first analog circuit 250 based on the STObias voltage Vsto (provided by STO bias voltage source 205) and ameasured STO bias current 160, where the baseline STO bias (alsoreferred to herein as the DC or low-frequency component) may bedetermined by the resistance value or firmware. At 415, a second analogcircuit or firmware 255 determines a STO bias kick current value (e.g.,indicating an amplitude of an AC component of the STO bias current 160)based on Rsto, a termination resistance, and either the STO bias voltageVsto or a STO voltage kick value. At 420, the STO bias current 160 isgenerated based at least in part on the STO bias current kick value. At425, the STO bias current 160 is provided to the STO 120. In someembodiments, the STO bias current 160 is provided to the STO 120 by apush-pull differential circuit (e.g., as described the context of FIG.4). In some embodiments, the STO bias current 160 is provided to the STO120 dependent on a write trigger (e.g., as shown in FIG. 7). The timingof the STO bias current 160 may be determined based on a positive writesignal transition and/or a negative write signal transition (e.g., thewrite current 162 shown in FIG. 6). The timing of the STO bias current120 may be programmable so that the STO bias kick occurs at a desiredtime. In some embodiments, the STO bias current 160 is delayed before itis provided to the STO 120 to adjust the timing of the STO bias kick(i.e., the AC or high-frequency component of the STO bias current 160)with respect to the write data signal timing (e.g., as shown in FIG. 7).At explained above, the characteristics of the STO bias current 160 andthe write current 162, including timing, may be jointly optimized. At430, the method ends.

FIG. 9 is a flowchart illustrating another method 450 of electricallybiasing a STO 120 in accordance with some embodiments. At 455, theprocess begins. At 460, the amplitude of a high-frequency component ofthe STO bias current 160 is determined. The high-frequency componentincludes Ikick. The amplitude of the high-frequency component may bedetermined using an intrinsic circuit or firmware (e.g., as illustratedin the embodiment of FIG. 5). At 465, the amplitude of a low-frequencycomponent of the STO bias current 160 is determined. The low-frequencycomponent may be simply a DC component, or it may include alow-frequency AC component (where “low-frequency” means that thefrequency of any AC component included in the low-frequency component islower than the frequency of the high-frequency component). The amplitudeof the low-frequency component may be determined using an intrinsiccircuit (e.g., as illustrated in FIG. 4) or firmware. At 470, theduration of the high-frequency component is optionally determined. Theduration of the high-frequency component may be expressed relative to aperiod of the high-frequency component (e.g., as a duty cycle) or inunits of time (e.g., picoseconds). If performed, block 470 may beperformed using firmware.

At 475, the high-frequency component of the STO bias current isgenerated (e.g., using the circuit shown in FIG. 4) based at least inpart on the amplitude of the high-frequency component determined atblock 460. Optionally, if optional block 470 was performed, thehigh-frequency component is further generated based on the durationdetermined at block 470. The high-frequency component may optionally begenerated based at least in part on a write trigger (as shown, forexample, in FIG. 7), which may be, for example, determined based on atleast one write signal transition. At 480, the low-frequency componentof the STO bias current 160 is generated based at least in part on theamplitude of the low-frequency component determined at block 465 (e.g.,using the circuit shown in FIG. 4). Optionally, the low-frequencycomponent may be generated further based on an indication that the harddisk drive is in a specified mode. For example, the low-frequencycomponent may be generated when the hard disk drive is in a write mode.Alternatively, or in addition, the low-frequency component may begenerated when the hard disk drive is in a mode that includes at leastone operation other than writing (e.g., reading). Optionally, at 485,the write current and either or both of the low-frequency component andthe high-frequency component are jointly optimized. At 490, thehigh-frequency and low-frequency components are provided to the STO 120.As explained in the discussion of FIG. 4, the low-frequency componentmay be generated using a current source or a voltage source. Thehigh-frequency component may be generated using a current source. At495, the method ends.

It is to be understood that some of the blocks shown in FIG. 9 may beperformed in a different order than illustrated. For example, block 465may be performed before, after, or at the same time as block 460.Similarly, if optional block 470 is performed, it may be performedbefore, after, or at the same time as either or both of blocks 460, 465.Furthermore, although block 475 must follow block 460, block 475 may beperformed before, after, or at the same time as blocks 465 and 480.Likewise, although block 480 must follow block 465, block 480 may beperformed before, after, or at the same time as blocks 460, 470 (ifperformed), and 475. Moreover, the optional joint optimization of thewrite current and the low-frequency and/or high-frequency component(s)of the STO bias current at block 485 may involve other blocks (e.g.,block 485 may include portions or all of blocks 460, 465, 470 (ifperformed), 475, and/or 480). Similarly, block 485 may iterate throughor repeat other blocks (e.g., block 485 may loop through some or all ofblocks 460, 465, 470 (if performed), 475, and/or 480). Thus, FIG. 9presents one exemplary ordering of the various blocks, includingoptional blocks. Alternative orderings are possible and are explicitlycontemplated herein.

In the foregoing description and in the accompanying drawings, specificterminology has been set forth to provide a thorough understanding ofthe disclosed embodiments. In some instances, the terminology ordrawings may imply specific details that are not required to practicethe invention.

To avoid obscuring the present disclosure unnecessarily, well-knowncomponents (e.g., of a disk drive) are shown in block diagram formand/or are not discussed in detail or, in some cases, at all.

Unless otherwise specifically defined herein, all terms are to be giventheir broadest possible interpretation, including meanings implied fromthe specification and drawings and meanings understood by those skilledin the art and/or as defined in dictionaries, treatises, etc. As setforth explicitly herein, some terms may not comport with their ordinaryor customary meanings.

As used in the specification and the appended claims, the singular forms“a,” “an” and “the” do not exclude plural referents unless otherwisespecified. The word “or” is to be interpreted as inclusive unlessotherwise specified. Thus, the phrase “A or B” is to be interpreted asmeaning all of the following: “both A and B,” “A but not B,” and “B butnot A.” Any use of “and/or” herein does not mean that the word “or”alone connotes exclusivity.

As used in the specification and the appended claims, phrases of theform “at least one of A, B, and C,” “at least one of A, B, or C,” “oneor more of A, B, or C,” and “one or more of A, B, and C” areinterchangeable, and each encompasses all of the following meanings: “Aonly,” “B only,” “C only,” “A and B but not C,” “A and C but not B,” “Band C but not A,” and “all of A, B, and C.”

To the extent that the terms “include(s),” “having,” “has,” “with,” andvariants thereof are used in the detailed description or the claims,such terms are intended to be inclusive in a manner similar to the term“comprising,” i.e., meaning “including but not limited to.” The terms“exemplary” and “embodiment” are used to express examples, notpreferences or requirements.

The terms “over,” “under,” “between,” and “on” are used herein refer toa relative position of one feature with respect to other features. Forexample, one feature disposed “over” or “under” another feature may bedirectly in contact with the other feature or may have interveningmaterial. Moreover, one feature disposed “between” two features may bedirectly in contact with the two features or may have one or moreintervening features or materials. In contrast, a first feature “on” asecond feature is in contact with that second feature.

The drawings are not necessarily to scale, and the dimensions, shapes,and sizes of the features may differ substantially from how they aredepicted in the drawings.

Although specific embodiments have been disclosed, it will be evidentthat various modifications and changes may be made thereto withoutdeparting from the broader spirit and scope of the disclosure. Forexample, features or aspects of any of the embodiments may be applied,at least where practicable, in combination with any other of theembodiments or in place of counterpart features or aspects thereofAccordingly, the specification and drawings are to be regarded in anillustrative rather than a restrictive sense.

What is claimed is:
 1. An apparatus for electrically biasing aspin-torque oscillator (STO), the apparatus comprising: means fordetermining an amplitude of a high-frequency component of a biascurrent; means for determining an amplitude of a low-frequency componentof the bias current; means for generating the high-frequency componentbased at least in part on the determined amplitude of the high-frequencycomponent; means for generating the low-frequency component based atleast in part on the determined amplitude of the low-frequencycomponent; means for providing the high-frequency component to the STO;and means for providing the low-frequency component to the STO.
 2. Theapparatus recited in claim 1, further comprising: means for programminga delay or an advance of the high-frequency component before providingthe high-frequency component to the STO.
 3. The apparatus recited inclaim 1, further comprising: means for jointly optimizing (a) a writecurrent for writing to a magnetic medium and (b) at least one of thelow-frequency component or the high-frequency component.
 4. Theapparatus recited in claim 1, wherein generating the high-frequencycomponent is further based at least in part on a signal trigger, whereinthe signal trigger is determined based on at least one write signaltransition.
 5. The apparatus recited in claim 1, wherein the means fordetermining the amplitude of the high-frequency component comprisefirmware configured to calculate the amplitude of the high-frequencycomponent based at least in part on a STO resistance value.
 6. Theapparatus recited in claim 1, wherein the means for determining theamplitude of the high-frequency component comprise a circuit.
 7. Theapparatus recited in claim 1, further comprising: means for determininga duration of the high-frequency component.
 8. The apparatus recited inclaim 7, wherein the means for determining the duration of thehigh-frequency component comprise firmware.
 9. The apparatus recited inclaim 1, wherein generating the low-frequency component is further basedat least in part on an indication that the data storage device is in aspecified mode.
 10. The apparatus recited in claim 9, wherein thespecified mode is a write mode.
 11. The apparatus recited in claim 9,wherein the specified mode includes at least one operation other thanwriting.
 12. The apparatus recited in claim 1, wherein the means fordetermining the amplitude of the low-frequency component comprisefirmware configured to calculate the amplitude of the low-frequencycomponent based at least in part on a STO resistance value.
 13. Theapparatus recited in claim 1, wherein the means for determining theamplitude of the low-frequency component comprise a circuit.
 14. Theapparatus recited in claim 1, further comprising: means for jointlyoptimizing (a) a write current for writing to a magnetic medium and (b)at least one of the low-frequency component or the high-frequencycomponent.
 15. The apparatus recited in claim 1, further comprising:means for programming at least one characteristic of the high-frequencycomponent before providing the high-frequency component to the STO. 16.The apparatus recited in claim 15, wherein the at least onecharacteristic comprises a delay, an advance, a timing, the amplitude,or a duration of the high-frequency component.
 17. A data storage devicecomprising the apparatus recited in claim
 1. 18. An apparatus forelectrically biasing a spin-torque oscillator (STO), the apparatuscomprising: means for determining, using a first analog circuit, aresistance of the STO based on a STO bias voltage and a measured STObias current; means for determining a STO bias kick current value basedon (a) the resistance of the STO, (b) a termination resistance, and (c)either the STO bias voltage or a STO voltage kick value; means forgenerating the bias current based at least in part on the STO biascurrent kick value; and means for providing the bias current to the STO.19. The apparatus recited in claim 18, further comprising: means forprogramming a timing of the current kick.
 20. A data storage devicecomprising the apparatus recited in claim 18.